SCIENCE EVENTS

In an article recently published in Physical Review Letters, Ketterle's group describes the collapse of large homogeneous Bose-Einstein condensates due to attractive interactions that they turn on rapidly. They seed the BEC cloud with a certain momentum state, then they suddenly switch the cloud into a state with a negative scattering length using a nearby Feshbach resonance. This technique allows them to cause a local instability and to observe the amplification of the instability into the collapse. They are also able to observe the appearance of the state conjugate to the seed state as required by momentum conservation in the atom system. For more details, see Amplification of Local Instabilities in a Bose-Einstein Condensate with Attractive Interactions. Phys. Rev. Lett. 90, 160405 (2003), authors J.K. Chin, J.M. Vogels, and W. Ketterle.

Another article in PRL describes vortices in BEC without cores. In Coreless vortex formation in a spinor Bose-Einstein condensate by A.E. Leanhardt, Y. Shin, D. Kielpinski, D.E. Pritchard, and W. Ketterle, (Phys. Rev. Lett. 90, 140403 (2003)), the group reports the process by which vortices are caused to form in sodium clouds in the BEC state. The process is best described by the caption to the following figure.

Coreless vortex formation in a spinor Bose-Einstein condensate. Coreless vortices are imprinted by ramping Bz to zero and were diagnosed by suddenly switching Bz << 0 (a-d) and Bz >> 0 (e-h). Axial absorption images display the optical density of condensates after 20 milliseconds of ballistic expansion a,e without and b,f with a magnetic field gradient applied to separate different spin states. c,g show azimuthally averaged optical density vs. radial position for spin components shown in b,f. The radial separation of the spin states resulted from their relative phase windings and is a clear signature of the skyrmion/meron wave function. d,h show the axial magnetization per particle vs. radial position.